1. Field of the Invention
The present invention relates to a semiconductor device including a plurality of semiconductor substrates attached with each other. The present invention also relates a method of manufacturing a semiconductor device.
2. Description of the Related Art
A semiconductor device including a base substrate, various elements disposed at a surface portion of the base substrate, and a sealing cap disposed above the elements for protecting the elements and a method of manufacturing the semiconductor device are disclosed, for example, in JP-A-2004-333133, U.S. Pat. No. 6,936,491 and U.S. Pat. No. 7,153,718.
A semiconductor device disclosed in JP-A-2004-333133 will be described with reference to FIG. 9A and FIG. 9B. The semiconductor device is an inertial force sensor. For the sake of convenience, a right-left direction in FIG. 9A and FIG. 9B is called as a first direction, and an upper-lower direction in FIG. 9A perpendicular to the first direction is called as a second direction.
The inertial force sensor includes a device layer 11. In the device layer 11, springs 1, anchors 2, beams 3, island electrodes 7a and 7b, and a frame 10 are integrally formed. A lower surface of the device layer 11 is bonded to a lower substrate 12. An upper surface of the device layer 11 is bonded to an upper substrate 13. The device layer 11 is hermetically-sealed by the lower substrate 12 and the upper substrate 13.
The island electrodes 7a are configured to electrically couple movable electrodes 5 to an external device. The island electrodes 7b are configured to electrically couple fixed electrodes 6 to an external device. On an upper surface of each of the island electrodes 7a and 7b, an electrode pad 8 to be coupled with an external device is attached. The upper substrate 13 has through holes 9 at portions corresponding to the electrode pads 8 on the island electrodes 7a and 7b. Each of the electrode pads 8 is electrically coupled with an external device (not shown) such as an integrated circuit (IC) through a bonding wire passing through the through hole 9
The anchors 2 are fixed to the lower substrate 12. The island electrode 7a and 7b and the frame 10 are fixed to both of the lower substrate 12 and the upper substrate 13. The springs 1, the beams 3 and a mass body 4 are not fixed to the lower substrate 12 and the upper substrate 13. Each of the beams 3 is held by the corresponding one of the anchors 2. The mass body 4 is held by the beams 3 to be movable in the horizontal direction. Each of the springs 1 electrically couples one of the anchors 2 and a corresponding one of the island electrodes 7a. 
In the second direction, the movable electrodes 5 are attached to two sides of the mass body 4. The fixed electrodes 6 are attached to each of the island electrodes 7b. At the two side of the mass body 4, the movable electrodes 5 are opposite the fixed electrodes 6 in the first direction. When the inertial force sensor receives inertial force in the first direction, the mass body 4 moves in the first direction due to the inertial force, distances between the movable electrodes 5 and the fixed electrodes 6 change, and an electrostatic capacity between the movable electrodes 5 and the fixed electrodes 6 changes. By detecting the change in the electrostatic capacity, the inertial force applied to the inertial force sensor can be detected.
In the inertial force sensor, the island electrodes 7a and 7b are insulated from each other. The movable electrodes 5 attached to the mass body 4 are electrically coupled with the island electrodes 7a through the beams 3, the anchors 2, and the springs 1. The island electrodes 7a are electrically coupled with an external device such as an IC through the electrode pads 8 and the bonding wires passing through the through holes 9. The fixed electrodes 6 attached to the island electrodes 7b are electrically coupled with en external device such as an IC through the island electrodes 7b, the electrode pads 8 disposed on the island electrodes 7b and the bonding wires passing through the through holes 9.
In the semiconductor device illustrated in FIG. 9A and FIG. 9B, an inertial force sensor element provided at the device layer 11 is protected by being hermetically-sealed by the lower substrate 12 and the upper substrate 13. The lower substrate 12 and the upper substrate 13 are used only for configurating the above-described sealing structure. In order to effectively use the lower substrate 12 and the upper substrate 13, a control circuit of the inertial force sensor element can be formed as long as the lower substrate 12 and the upper substrate 13 can seal the inertial force sensor element.
In the semiconductor device illustrated in FIG. 9A and FIG. 9B, each of the bonding wires is passed through one of the through holes 9 provided in the upper substrate 13 and is bonded to one of the electrode pads 8 on the island electrodes 7a and 7b so as to electrically couple the island electrodes 7a and 7b to the external device such as the IC. In order to bond the bonding wires, the upper substrate 13 is required to have large through holes 9 so that a bonding tool does not come in contact with the upper substrate 13. Thus, a dimension of a chip may increase and a production cost may increase. In addition, it is difficult to secure an insulating property with certainty after bonding and it is difficult to perform a wire bonding when the semiconductor device has a complicated three-dimensional wiring structure such as, for example, when a circuit is formed in the lower substrate 12 and the upper substrate 13.